Phase change mechanism

ABSTRACT

In a phase change mechanism in which the phase of a driven member ( 10 ) relative to a drive member ( 12 ) is adjusted by axial displacement of an actuating rod ( 30 ) connected to the piston ( 50 ) of a hydraulic jack rotatable with the drive and driven members, the cylinder ( 52 ) of the hydraulic jack has a double-skinned wall, and the gap ( 54 ) between the two skins of the cylinder wall serves as a passage for supplying oil to and from one of the working chambers of the hydraulic jack.

FIELD OF THE INVENTION

The present invention relates to a phase change mechanism for an enginecamshaft to enable the valve timing of the engine to be varied to suitdifferent operating conditions.

BACKGROUND OF THE INVENTION

As Is well known, valve timing has a significant effect on engineperformance and the optimum setting varies with engine operatingconditions. To optimise performance under different operatingconditions, it is necessary to be able to vary the valve timing. Complexsystems have been proposed that vary the duration of valve events, thisbeing equivalent to using a cam with a different profile, while othersystems only vary the phase of a camshaft acting on one set of valvesrelative to the engine crankshaft and/or relative to a second camshaftacting on the remaining valves.

Various phase change mechanisms have been proposed in the past but theyhave suffered from various problems. Some, though feasible, have beencostly to implement while other have developed excessive friction or notproved to be reliable. Furthermore, many could not be fitted as amodification to existing engines as they required much of the valvetrain and cylinder head to be redesigned.

The Applicants' earlier EP-A-0 733 154 discloses a valve operatingmechanism comprising a hollow shaft, a sleeve journalled on the hollowshaft and fast in rotation with a cam, a coupling yoke connected by afirst pivot pin to the hollow shaft and by a second pivot pin to thesleeve and means for moving the yoke radially to effect a phase changebetween the hollow shaft and the sleeve. The means for moving the yokeradially comprise an actuating rod slidably received in the hollowshaft, a cam surface on the actuating rod and a plunger passing througha generally radial bore in the hollow sleeve to cause the yoke to moveradially in response to axial movement of the actuating rod.

The above valve operating mechanism is only one example in which a phasechange is brought about by axial movement of an actuating rod relativeto the camshaft. Other phase change mechanisms that use an actuating rodmovable axially relative to the camshaft are also known. The presentinvention is particularly concerned with a hydraulic actuator fordisplacing the actuating rod of such a phase l5 change mechanism.

It has already been proposed to mount a hydraulic jack on the drivepulley or sprocket of the camshaft and to connect the actuating rod ofthe piston of the hydraulic jack. The most common prior art proposal forsupplying oil to the hydraulic jack employs drillings in the camshaft.In such a case, however, the length of the drillings and therestrictions placed on their diameter, make it difficult to ensure anadequate supply of oil to the hydraulic jack to allow the phase of thecamshaft to be adjusted rapidly.

Summary of the invention

With a view to mitigating the foregoing disadvantage, the presentinvention provides a phase change mechanism in which the phase of adriven member relative to a drive member is adjusted by axialdisplacement of an actuating rod connected to the piston of a hydraulicjack rotatable with the drive and driven members, wherein the cylinderof the hydraulic jack has a double-skinned wall, and the gap between thetwo skins of the cylinder wall serves as a passage for supplying oil toand from one of the working chambers of the hydraulic jack.

Preferably, the end of the cylinder remote from the drive and drivenmembers communicates with supply and return passages in a stationaryengine cover or spider, one passage lying in line with the axis ofrotation of the drive and driven members and communicating directly witha first working chamber of the hydraulic jack and the other passagecommunicating with the other working chamber of the hydraulic jack byway of the gap between the two skins of the cylinder wall.

The invention allows oil passages of large flow through is cross sectionto be employed while retaining the benefit of a compact design thatallows the phase change mechanism to be retrofitted to existing engines.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described further, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a section through a camshaft fitted with a phase changemechanism, taken through a plane passing through the rotational axis,

FIG. 2 is section along the line II—II in FIG. 1,

FIG. 3 is section along the line III—III in FIG. 2,

FIG. 4 is a section along the line IV—IV in FIG. 3, and

FIG. 5 is schematic less detailed section similar to that of FIG. 1 butshowing an alternative embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIGS. 1 to 4, a camshaft 10 is driven by a drive pulley 12 to which atoothed ring 14 is attached by means of bolts 16 to allow the camshaft10 to be driven from the engine crankshaft by means of a toothed belt.The drive pulley 12 is journalled on the camshaft 10 and is retainedaxially on the camshaft 10 by being captive between a collar 11projecting from the camshaft 10 and a washer 13 that is held in place onthe camshaft 10 by a circlip 15.

Torque is transmitted from the pulley 12 to the camshaft 10 by means ofa phase change mechanism that comprises a transverse pin 18 located in aflat 20 in the camshaft and a yoke 22 fast in rotation with the drivepulley 12. As seen in FIG. 2, the pin 18 has at its opposite ends twoshoes 24 that engage a contoured inner surface of the yoke 22. The shoes24 are spring-biased so that the pin 18 simultaneously contacts the yoke22 and the shoulder of the Flat 20 of the camshaft 10 to transmit torquefrom the yoke 22 to the camshaft 10.

It will be clear also from FIG. 2 that the phase of the camshaft 10relative to the drive pulley 12 depends on the position of the pin 18and that by moving the pin 18 from side to side in FIG. 2 the phase ofthe camshaft 10 relative to the drive pulley 12 may be changed.

To vary the phase between the camshaft 10 and the drive pulley 12, anaxially displaceable actuating rod 30 is located in a blind bore 32 inthe end of the camshaft 10. The actuating rod 30 is formed with a flaton which there are located two wedges 36, 38 that are best shown in thesectional plane of FIG. 3. The wedges 36 and 38 taper in oppositedirections and thus define between them a gap 40 that is inclinedrelative to the rotational axis. A tooth 42 of the transverse pin 18 islocated in the gap 40 such that when the actuating rod 30 is movedaxially the pin 18 is moved from side to side. In order to avoidbacklash a spring 44, also shown in the section of FIG. 4, urges thewedge 38 in an axial direction in a sense to reduce the width of the gap40 and ensure that the tooth 42 makes surface contact with both wedges36 and 38 simultaneously.

To bring about axial movement of the actuating rod 30 the end of thelatter projecting beyond the front end of the drive pulley 12 isconnected to a piston 50 reciprocable within a cylinder 52. The wall ofthe cylinder 52 is double skinned, there being an annular gap 54 betweenthe inner and outer skins of the cylinder. The double skinned cylinder52 is formed by inserting one cup of pressed steel into another and agap 54 remains around the periphery of the inner cup to act as an oilpassage, to permit oil to flow to the working chamber lying to the rightof the piston 50 as viewed in FIGS. 1 and 3. The cylinder 52 is mountedin a recess in the front of the drive pulley 12 with its outer skinsealed by an O-ring 70 relative to the recess and is retained within therecess by a circlip 72. The inner skin of the cylinder only contacts therecess at a few points about its periphery, leading a gap of largethrough flow cross section through which oil may flow into the workingchamber lying to the right of the piston 50, as viewed.

The engine is fitted with a stationary front cover 60 or a spider havingsupply and return oil passages 62 and 64 leading to a connection socketthat fits over the end of the double skinned cylinder 52. Rotary seals66 and 68 in the cover 60 seal against the inner and outer surfaces ofthe cylinder 52. In this way, oil is supplied directly from the oilpassage 62 to the working chamber shown to the left of the piston 50,while oil passes from the passage 64 through the gap 54 to the workingchamber lying the right of the piston 50 as viewed. This configurationallows oil passage of large through flow cross section to be usedthereby enabling rapid adjustment of the axial position of the actuatingrod 30 and the application of a sufficient force to overcome anyfrictional force on the actuating rod.

The camshaft of FIG. 5 differs from that of FIGS. 1 to 4 in that asingle phase change mechanism is used to alter the phase of twodifferent camshafts relative to the engine crankshaft. The essentialdifference resides in that the camshaft 10′ has two sprockets 12 a′ and12 b′ journalled on it instead of only one. The sprocket 12 a′ isequivalent to the drive pulley 12 in FIGS. 1 to 4 and the transmissionof torque from the crankshaft through the sprocket 12 a to the camshaft10′ is exactly the same as previously described. The second sprocket 12bis used to transmit torque from the camshaft 10′ to a second camshaft(not shown) by way of a chain or toothed belt. The second sprocket 12 b′is coupled to the camshaft 10′ by means of a second yoke, transverse pinand wedges on the opposite side of the actuating rod 30′ that areessentially those previously described. In this manner, when theactuating rod is displaced axially the sprocket 12 a′ is phase shiftedin one direction while the sprocket 12 b′ is phase shifted in theopposite direction. This arrangement therefore allows a single hydraulicjack acting on only one actuating rod to bring about a change of phaseof one camshaft in one direction relative to the engine crankshaft and aphase change of a second camshaft in the opposite sense.

The two phase changes need not necessarily be equal as the extent of thephase change for a given axial displacement of the actuating rod willdepend on the tapering angle of the wedges and it is possible for thetwo sets of wedges to have different angles of taper.

It will be appreciated that the invention is not restricted to theparticular form of phase change mechanism described above but may beapplied to any mechanism, for example that in EP-A-0 733 154, thatrelies on axial displacement of an actuating rod to effect a phasechange.

What is claimed is:
 1. A phase change mechanism in which the phase of a driven member (12) relative to a drive member (10) is ni adjusted by axial displacement of an actuating rod (30) iconnected to the piston (50) of a hydraulic jack rotatable with the drive and driven members (12, 10), characterised in that the cylinder (52) of the hydraulic jack has a double-skinned wall, and the gap between the two skins of the 10 cylinder wall serves as a passage for supplying oil to and from one of the working chambers of the hydraulic jack.
 2. A phase change mechanism as claimed in clarify 1, wherein the end of the cylinder (52) remote from the drive and driven members (12, 10) communicates with supply and return passages (62, 64) in a stationary engine cover (60) or spider, one passage (62) lying in line with the axis of rotation of the drive and driven members (12, 10) and communicating directly with a first working chamber to the hydraulic jack and the other passage (64) communicating with the other working chamber of the hydraulic jack by way of the gap between the two skins of the cylinder wall.
 3. A phase change mechanism as claimed in claim 2, wherein the end of the cylinder (52) is received in a socket in the engine cover (60) or spider that comprises rotary seals (66, 68) for sealing against the cylinder. 